This has been a very interesting thread, I also have had the same problem for years and it was this reason I went to QAYG
I have a Janome 6500, could one of you helpful lady's and gentleman tell me what foot pressure you have when doing SITD please
I must admit my juki is much better at sewing in the ditch but still have one or two puckers,but I am going to try pushing the fabric towards the walking foot